The present invention relates to an oil-pressure determination apparatus of an engine.
An oil pump to supply oil for lubricating or cooling to engine components is driven by an engine. Herein, if the pressure of the oil decreases to an improperly-low oil pressure, there is a concern that an engine seizure may occur. Accordingly, in general, an oil pressure switch is provided in an oil passage downstream of the engine pump to warn such a situation of the oil pressure's decreasing improperly. The oil pressure switch is activated to a conductive state in response to a specified setting oil-pressure (threshold). Herein, this specified setting oil-pressure (threshold) is generally set at a low pressure so that the above-described decrease of the oil pressure can be properly detected even in an idling operation of the engine.
However, this setting of the specified setting oil-pressure at the low pressure causes a problem in that an operation of the oil pressure switch may be easily influenced by fluctuation in oil pressure in response to changes of the engine operating state or the vehicle traveling state. That is, there is a possibility that the state of the oil pressure switch may change between the conductive state and the non-conductive state thereof repeatedly even though the oil pressure has no abnormality, thereby making a warning lump flash improperly. Accordingly, a vehicle driver may feel uneasy. In this regard, U.S. Pat. No. 5,229,745 discloses a technology in which even though the state of the oil pressure switch changes to the conductive state (i.e., shortage of the oil pressure), any warning is not given until a specified time has passed from the timing the engine starts. On the other hand, after the specified time has passed, once the state of the oil pressure switch changes to the conductive state, the warning is maintained despite the state of the oil pressure switch changing to the non-conductive state.
In order to solve the above-described problem of the inappropriate influence of the oil pressure fluctuation on the oil pressure switch, it may be considered that the above-described setting oil-pressure of the oil pressure switch is set at a high pressure instead of relying on the technology of the above-described patent document. However, the oil pressure is generally influenced by the viscosity of the oil, i.e., the temperature of the oil, so that in a case in which the temperature is relatively high, the oil pressure may not increase up to the setting oil-pressure of the oil pressure switch unless the engine speed increases to some extent, compared with a case in which the temperature is relatively low. Therefore, in order to properly determine a state of the oil pressure regardless of the level of the temperature, it may be necessary to detect an operation state of the oil pressure switch at the timing the engine speed increases above a specified speed (2500 rpm, for example). This means that the oil-pressure state cannot be properly determined in a whole engine operation range covering the practical speeds of the engine, including the idling speed of the engine, that is, that the determination in the engine operation rage of the low speed needs to be excluded. However, even when the engine speed is low, any malfunction of a circulation system may cause the engine seizure. Meanwhile, it may be considered that an oil-pressure sensor which can detect the oil pressure linearly is used, but the cost of this sensor may be generally high.